This report describes the concluding work on a series of studies concerned with determining, understanding, and trying to predict the behavior of polymethylmethacrylate (PMMA) and polycarbonate (PC) under impact. In the present work the impact velocity was extended to 2.1, 125, and 220 m/s using a 4.5 mm steel ball as the projectile. Because of dispersion effects the pulse detected using an instrumented Hopkinson impact bar was markedly distorted. A new semi-empirical procedure for correcting the pulse was developed that overcame difficulties encountered in the theoretical methods. Analysis of the data showed that the deduced Young's modulus of PMMA slowly increases with increasing impact velocity. However, the derived modulus of PC decreases by a factor of five when the impact velocity was increased from 2.1 to 220 m/s. This decrease in stiffness is unexpected and anomalous, but is beneficial to reducing the potential for impact damage. A theoretically-based model was formulated to 'predict' the impact response of the two materials from their elastic modulus, densification properties, and stress-relaxation laws. This modified spring/ dashpot model allows the response of the polymers to be continuously varied between series-like and parallel-like. The PMMA was found to require a predominantly series-like mode description, whereas the PC response was more parallel-like.